1. Field of the Invention
The present invention relates to information delivery system configured to encrypt information such as video content by electronic data and deliver the information to a user terminal device from a communication delivery device via a network.
2. Description of the Related Art
Recently, as broadband became widely used, services which deliver video content by electronic data in use of communication lines have become popular. In such services, a service, on condition that the service generates an encrypted key by using information specific to a medium such as a medium ID written in a read-only area in an information recording medium, encrypts the video content with the encrypted key to deliver the encrypted video content and uses a specified information recording medium for which a contract has been made among a delivery agent and a user, is made practicable.
More specifically, as regards the video delivery service, a service which encrypts video data by using an information recording medium corresponding to content protection for recordable media (CORM) or an advanced access content system (AACS) and delivers the encrypted video data has become widely used.
In this video content delivery service, the user loads an information recording medium (IC memory card [SD etc.], CD-R, CD-R/W, DVD-R, DVE-R/W, DVD+R, DVD+R/W, DVD-RAM, etc), for which the contract has been made, to user terminal devices, selects either a purchase type which can be permanently viewed like a commercially available DVD package or rental type which can be viewed for a limited time, and instructs delivery of arbitrary video content in a state in which the information specific to the recording medium has become readable. At this moment, the user terminal device presents the information specific to the loaded medium together with the information about the delivery request.
On the other hand, a delivery center device stores a plurality of video contents in a state in which the contents are encrypted with keys different from one another in order to prevent content distribution inside the center device, and manages each key separately from the contents. When receiving the information about the delivery request and the information specific to the loaded medium from the user terminal device, the center device encrypts the key which has encrypted the specified content by using the information specific to the loaded medium, and delivers the encrypted key to a request origin together with the specified content. Meanwhile, the user terminal device downloads the encrypted video content which has been delivered from the center device, decrypts the encrypted key by using the information specific to the loaded medium to be transmitted with the downloading, decrypts the encrypted video content by using the decrypted key and then makes a video viewable (refer, for example, to Jpn. Pat. Appln. KOKAI Publication No. 2004-350150 and Jpn. Pat. Appln. KOKAI Publication No. 2005-159752).
However, in the aforementioned operation form of the conventional video delivery service, when the user additionally records new content to pre-recorded content, both the contents are stored in a state in which the respective contents are encrypted with different keys each other. Therefore, a switching period for the keys is needed in continuous reproduction. In the CPRM, since only one piece of content may be managed for information specific to one medium, the CPRM may not perform additional writing basically. To improve such a problem, it is needed to individually decrypt each content once at each time and encrypt again after connection processing, and this procedure forces the user to treat a heavy load.
As mentioned above, in an information delivery system represented by the conventional video delivery service, since the system utilizes an information recording medium with specific information for copyright protection added thereto and downloads data encrypted in a form, in which the data is related to the recording medium, and stores the data in a recording medium, it is hard to additionally record the encrypted data to be related to the same recording medium, on the pre-recorded medium.